The questions to be examined in this proposal are: 1) What is the nature of gene function during the mammalian cell cycle, i.e., do most genes function continuously or periodically? 2) If most genes function continuously in mammalian cells, do those genes involved in activating a cell for DNA synthesis function periodically? 3) What is the relationship between DNA synthesis and cell division? These questions will be investigated primarily through the use of DNA-RNA hybridization studies involving the non-repeated sequences of DNA.